Project Information

Summary:

We proposed to demonstrate long-term establishment of the predatory midge, Feltiella acarisuga, to control spider mites in greenhouse tomatoes using a banker plant system consisting of the Banks grass mite (BGM) on corn. We worked with 4 farms in 3 states, as well as a private crop consultant and an extension agent.

Feltiella colonization of the BGM banker plants occurred, but was at very low levels. Scouts had to search the banker plants carefully in order to find just a few Feltiella. In addition, the corn plants turned brown and died within weeks, overwhelmed by the mites and overcrowded in the pots.

An alarming result of the study was the observation that the Banks Grass Mite damaged the bean leaves as well as the corn leaves. We had not been aware that this mite could attack broad leaved plants until that happened.

Two positive outcomes of the study were

bean trap plants were demonstrated at all 4 sites, and were indicators of both two spotted spider mites and Feltiella, and

Feltiella was demonstrated readily colonizing both the control and the treated greenhouses.

Introduction:

We proposed to introduce a spider mite that is not a pest of tomatoes in order to supply prey to support early introductions of predators, thereby preventing later-season Two-spotted Spider Mite (TSSM) outbreaks.

We understood that Banks’ grass mites (Oligonychus pratensis, BGM) will grow on corn, millet or barley, but cannot reproduce on broadleaved plants. With a stable prey population, we hoped to see season-long mite prevention with only a few releases of predators.

An important, naturally occurring predator of spider mites, the predatory gall midge Feltiella acarisuga, can find isolated pockets of two-spotted spider mites (TSSM), control them and reproduce in a variety of crops. However, it is most effective at preventing outbreaks when TSSM populations are low—typically before TSSM damage becomes evident in tomatoes.

The objective of the project was to demonstrate long-term establishment of predatory midges using a banker plant system and concomitant pest suppression. We also hoped to demonstrate an overall reduction of costs (including materials, equipment costs, and labor in applying controls and scouting) by comparing treated houses to untreated houses.

Banker plants are already widely utilized for aphid control, though less so for other pests. Much of the earliest research done with banker plants for mite control focused on allowing TSSM to reproduce on plants especially prone to TSSM infestations, which many growers are reluctant to do. The mite hot spots act as nurseries for predatory mites, increasing predatory mite abundance and associated pest control. Early work focused on ornamental plants, but adoption of bush beans as indicator/banker plants is gaining some traction in edibles production.

The most recent work with banker plants for BGM has been performed at the Mid-Florida Research and Education Center by Dr. Lance Osborne, who promotes wider adoption of this innovation. Currently, these banker plants are used in ornamental plant production in Florida. While Dr. Osborne has successfully used this system to support all spider mite predators, growers have only used predatory mites.

Feltiella acarisuga is a useful spider mite control in protected culture, and works well in tomatoes despite the glandular hairs that impede many biocontrols. A single release is often sufficient for season-long control, but it needs to coincide with the first mites arriving on the crop. The searching behavior of this insect is highly effective, being able to locate small, isolated populations of spider mites quickly. In addition to documenting said searching abilities, Dr. Osborne reports that natural populations of Feltiella find and colonize banker plants hosting BGM.

This project builds upon an already strong working knowledge of the organisms involved. The midges will establish on the banker plants in the high tunnel before mites are spotted on the crop, thereby being present when TSSM arrive. Using Feltiella rather than predatory mites should make the system easier to use, as evidence of Feltiella activity is easier to monitor and midges find TSSM on their own.

List of collaboration farmers and partners:

Eve Kaplan-Wlbrecht, Farmer

James Markey, Farmer

Jill Rotondo, Farmer

Nathan Ludlow, Farmer

Nicholas Ellis, Consultant

Sandra Menasha, Subcontractor

Project Objectives:

We propose using a banker plant system—corn infested with non-pest mites, Banks’ Grass Mite (BGM)—to support early establishment of TSSM predators, which will suppress TSSM later in the season. Four farms in three states will participate, each farm possessing a treatment and control house. After planting banker plants in treated structures and infesting with BGM, Feltiella acarisuga, a naturally-occurring TSSM predator, will be released and their reproduction on banker plants will be reported. To assess TSSM populations in the structure, we will use indicator plants for weekly observations of TSSM numbers as well as presence of Feltiella.

TSSM on tomatoes was to be observed subjectively. Costs associated with TSSM control was to be calculated and compared between treated and control houses. Outreach was to consist heavily of informal communications with growers, as IPM Labs, Cornell Cooperative Extension and collaborating growers are well tied into the Northeastern farming community. To supplement this, we proposed printing pamphlets to circulate and make several presentations in four states.

Research

Materials and methods:

Methods varied among cooperators. Below are the general guidelines for the project followed by variations among farms.

Corn Plants

The organic (non-gmo) corn seed 2015 Fertrell F 5250 SG, F 5250A SG(MF), and F 5250A SG(SF) seed was purchased from Larry Moore. The seed cost $15 per pound. The three types of corn were mixed and approximately 7 cups of seed were shipped to each grower April 11, 2016. Approximately 5 cups of seed remained at IPM Labs Inc. for testing seedling emergence, BGM compatibility, and stored as extra seed for the project. By day four of the emergence test 95% of the seedlings emerged.

It was not certain how the banker plants would fare in the greenhouse. Therefore recommendations changed with experience. The banker plants needed to survive long enough to support mite reproduction and survival so that the Feltiella will have enough to eat. Once the plants died, the mites were somewhat hardy and they could rebound given new plants. However, a suppressed mite population would not support many Felitella.

Larger, older corn plants would host more BGM and thus more Feltiella. The earlier corn plants are started, the better the mite production will be. This proposal uses the energy of the seedling, plus frequent plantings to keep the mites increasing.

Four pots of corn were planted weekly (1/8 cup of corn seed per 10 inch pot is about 100 seeds per pot). Pots were marked with the planting date and stored separate from the banker plant area to avoid immediate mite transfer and plant mortality. Corn was watered well and regularly. Although corn does thrive in dry conditions, the corn was planted very densely and required much more water than a normal corn plant.

Infesting the corn with Banks grass mite shipped from IPM Labs

Corn plants were seeded on a Monday and BGM on cut leaves were scheduled to arrive approximately 10 days later. When BGM arrived at the farm, 1/4 of the cut leaves were placed on each of the pots of corn. One pot was placed in a cage to protect it from predators. The other pots were moved to the greenhouse and bottom watered to avoid removing mites.

Continuous Mite Production

When the new corn was about 6 inches high, 3 pots are placed in the banker plant area and one pot into the cage. One uncaged, mite-infested pot was completely cut back and evenly distributed among the 3 uncaged plants. If the older corn looked like it was dying off and would not support the mites and predators for another week, all pots were cut back and distributed at a 1:1 ratio from old corn pot to new corn pot. The corn was then bottom watered. A bridge made of cotton string may be used to facilitate the transfer of mites between leaves.

Caged Corn

Some corn was caged with the BGM to protect the colony from unexpected predators. One new plant was rotated into the cage each week by cutting half the leaves off the older plant and placing them on the new plant. The other half of the leaves were placed in the greenhouse as extra food for Feltiella.

Adding the predator

Feltiella must have a high population of spider mites to eat. Two hundred and fifty Feltiella were released 1 week after BGM populations were present at high levels. The predator was released by opening the container and placing it in the banker plants. Midges were protected from drowning by orienting the container away from the flow of water.

Reporting Data

For all banker plants cooperators reported the presence or absence of BGM as well as BGM average count on 10 leaves (0-10, 20+, 50+). Feltiella larva, pupa, and adult counts were observed on banker plants, tomatoes and bush beans. The plants used for Feltiella counts were not specified. Some cooperators counted Feltiella on banker plants only while other included bush beans and tomatoes in their data collection. TSSM severity was on bush beans and tomatoes and was rated on a scale of 0-3 (0 = no damage, 1 = some stippling, 2 = heavy stippling and browning, 3 = leaves dying).

The Snap Beans

Snap beans are great indicators of spider mites. In a tomato greenhouse, they normally show spider mite damage long before the spider mites are seen on the tomatoes. Beans were used to indicate when the spider mites first appear in both greenhouses as well as document effect of Feltiella on the two spotted spider mites. 1 pot of beans was used for every 1000 sq ft of growing space in both the untreated house and the banker plant house. There were 6 bean seeds per pot. New pots were planted if the first pots started to fail from old age.

Cooperators:

James Markey: BGM were shipped on week 19. After BGM became established Feltiella were shipped to the farm weeks 23 and 27 (Table 2). The banks grass mite populations remained in good health on corn. Feltiella were not observed on the corn. When TSSM populations began to rise on green beans P. persimilis were used to control the pest population (Table 2). Feltiella were observed on tomato plants week 29 in both tunnels. J-Mar recorded TSSM Severity for weeks 29, 30 and 31. During this time observations were made in tunnel 1 on 0-2 banker plants, 1 bush bean, and 1 tomato per week. Observations in tunnel 2 were made on 1 bush bean and 1 tomato per week.

Intervale: Four pots of corn were planted per week and moved to the high tunnels when the leaves were about 6 inches tall. The corn was placed next to infested plants, an alternative to the cut leaves method, and leaves were in contact with the infested plants. Some BGM moved from older, infested material to the new growth when the older corn died. BGM were shipped on week 17 (Table 2). After BGM became established Feltiella were shipped to the farm week 23, 27, and 28 (Table 2). Observations were recorded for weeks 31 and 32 in tunnel 1 on 3-4 banker plants, 3-4 bush beans, and 1 tomato plant per week. In tunnel 2 observations were made on 1-2 bush beans and 1 tomato plant per week. Average TSSM severity results were analyzed.

Garden of Eve: Feltiella were shipped week 23 and 28 (Table 2). TSSM severity was observed weeks 27, 28, 30, 31, 32, and 34. Observations were made on 4 banker plants, 1 bush bean, and 1 tomato each week in tunnel 1, and 1 tomato per week in tunnel 2. Predatory mites were recorded in tunnel 1 on bush beans on week 32.

Ludlow: BGM were shipped to the farm week 26. Feltiella were shipped week 28. TSSM severity observations were made every other week for weeks 28-34 on 4 banker plants, 1 bush bean and 1 tomato plant in tunnel 1, and 1 tomato plant in tunnel 2.

Table 1: Tunnel Site Data

Tunnel Site Data

CATEGORY

TUNNEL 1

(CONTROL)

TUNNEL 2

(TREATMENT)

James Markey

Dimensions

W x L (feet)

15 x 100

26 x 100

Tomato

Variety

BHN 589

BHN 589

Other

Plants

Morning glory

Unidentified grass weeds

Tomato

Planting Date

Early April

Early April

Bean

Planting Date

1st week of April

1st week of April

Corn

Planting Dates

—

1st week of April

Then weekly through June 30

Feltiella Release

Dates

—

Mid-June & 7-July

Table 2. BGM Methods Timetable

BGM Methods Timetable

Grower

Week Number

Activity

Intervale

17

Corn started emerging

19

10,000+ BGM shipped on cut leaves

23

Corn approximately 6 in tall

23

250 Feltiella shipped (Koppert)

23

Carol visited and observed many mites and a few Stethorus beetles on the corn

27

250 Feltiella shipped (Biobest)

28

250 Feltiella shipped (Biobest)

31

Carol visited and observed hundreds of tiny predatory beetle adults and larvae on banker plants, as well as 1 dead Feltiella larva. Many feltiella larvae and pupae on bean plants in the treated and control houses, no spider mites on tomatoes, no predatory beetles on beans, and large orange and black lady beetle larvae on banker plants

Feltiella was observed at most sites in both the controls and the treatments and on the tomatoes and bush beans as well as on the banker plants (Table 3). It’s presence on the banker plants was just here and there, not at the abundant level we were hoping for. Presence or absence of Feltiella on tomato plants was more of an indication of presence or absence of spider mites on those plants, and not an indication of the level of control being exerted by the predators.

Table 3. Locations of Feltiella observations for the four cooperators.

Feltiella Observation Sites

Cooperator

Greenhouse

Plant

James Markey

Control

Tomatoes

James Markey

Treatment

Tomatoes

Intervale

Treatment

Banker Plant, Bush Beans

Intervale

Control

Bush Beans, Tomatoes

Garden of Eve

Treatment

Banker Plant, Bush Beans, Tomatoes

Ludlow

Control

Tomatoes

Ludlow

Treatment

Banker Plant, Bush Beans

Alternative plants and predators for the banker plant system should be considered. Throughout the experiment small predatory beetles naturally colonized some BGM mite infested corn and may be good predators for this banker plant system. In all tunnels, except for Garden of Eve, Feltiella appeared on tomatoes and beans more often than the corn banker plant.

Sandy Menasha observed that the bean trap plants adjacent to the corn banker plants seemed to be damaged by the BGM. Back at IPM Labs, we tested BGM on snap beans and found that, indeed, the beans would support continuous reproduction of the BGM.

Each cooperator had a unique approach to the banker plant system due to availability and viability of biologicals, greenhouse set up, and variation due to the general structure of the instructions provided by IPM Labs. The results from each farm are reviewed individually below.

BGM at James Markey’s farm was present on banker plants at low levels (0-10). Feltiella larvae/pupae were observed on tomatoes in the control and treatment greenhouses (Table 3). TSSM severity is reported in Figure 1. TSSM severity over time on bush beans in the treatment greenhouse remained at level 3, and in the control greenhouse began at 3 and decreased over time. TSSM severity over time on tomatoes in the treatment greenhouse increased, then decreased, and in the control greenhouse remained at level 1. The absence of Feltiella on corn may be due to low BGM populations on the corn compared to TSSM populations on tomatoes, and/or lack of establishment of BGM on corn. If corn is not an appropriate banker plant for Feltiella populations, then an alternative plant should be considered. Feltiella occurred on tomatoes in the control tunnel and treatment tunnel on week 29. The source of the predator may have been IPM Labs shipments or naturally occurring. TSSM populations were high week 26 and had to be controlled by releasing the predatory mite Phytoseiulus persimilis. Overall the banker plants did not support early establishment of Feltiella (2 shipments of 250 Feltiella) and TSSM populations were not consistently suppressed.

Figure 1. J-mar TSSM severity on bush beans and tomatoes in the treatment and control greenhouses.

BGM at Intervale was present on banker plants at high levels (50+). Feltiella larvae/pupae were observed on banker plants (1 larva in a 2 week period) and bush beans in the treatment greenhouse, and bush beans and tomatoes in the control greenhouse (Table 3). Average TSSM severity is reported in Figure 2. TSSM severity over time on bush beans in the treatment greenhouse increased slightly from 0.25 to 0.33, and in the control greenhouse decreased over time from 2 to 1. Average TSSM severity on tomatoes in both greenhouses was 0. Feltiella (3 shipments of 250 Feltiella) utilized corn banker plants with high populations of BGM. TSSM severity on bush beans, used as an early indicator of TSSM, were consistently low in the treatment greenhouse, and started at a severity of 2 in the control tunnel. Although TSSM severity on tomato plants was the same for both tunnels, the bush bean results suggest that banker plant presence is associated with consistently low severity of TSSM, while banker plant absence is associated with varying TSSM severity levels. Hundreds of Stethorus adults and larvae were observed on banker plants on week 31 and may have been an important factor in TSSM management.

Figure 2. Intervale average TSSM severity on bush beans and tomatoes in the treatment and control greenhouses.

BGM at Garden of Eve was present on banker plants at various levels (0, 0-10, 20+) and populations generally decreased over time. Feltiella larvae/pupae were observed on banker plants, bush beans, and tomatoes in the treatment greenhouse (Table 3). TSSM severity is reported in Figure 3. TSSM severity over time on bush beans in the treatment greenhouse increased from 0 to 1 and remained constant at 1 for 4 weeks. TSSM severity over time on tomatoes in the treatment greenhouse increased from 0 to 1 and remained constant at 1 for 4 weeks, and in the control greenhouse remained 0 until week 34 where it increased to 1. The results suggest that the banker plant system with BGM levels of 0-10 and 20+ was successful in establishing Feltiella (2 shipments of 250 Feltiella) and maintaining low populations of TSSM.

Figure 3. Garden of Eve TSSM severity on bush beans and tomatoes in the treatment and control greenhouses.

BGM at Ludlow was present on banker plants throughout the project, beginning at 20+ week 28, increasing to 50+ week 32, and eventually decreasing to 0-10 week 34. Feltiella larvae/ pupae were observed on banker plants and bush beans in the treatment greenhouse, and larvae/pupae/adults were observed on tomatoes in the control greenhouse (Table 3). TSSM severity is reported in Figure 4. TSSM severity on bush beans in the treatment greenhouse remained at 1 except for week 32 where it decreased to 0. TSSM severity on tomatoes in the treatment greenhouse was 0 throughout the project, and in the control greenhouse remained at 1 except for week 34 where it increased to 2. The decreased TSSM severity on bush beans in the treatment greenhouse and increased TSSM severity on tomatoes in the control greenhouse on week 32 may indicate that the banker plant presence allowed predators to remain in the greenhouse and control TSSM during a time when TSSM severity increased (control). On week 34 both greenhouses had TSSM levels back to normal for the greenhouses, indicating that banker plants may not have played a role in controlling the TSSM population. It may be possible for the TSSM population to return to normal without banker plant use.

Figure 4. Ludlow TSSM severity on bush beans and tomatoes in the treatment and control greenhouses.

Research conclusions:

Feltiella colonization of the BGM banker plants occurred, but was rare. Scouts had to search the banker plants carefully in order to find just a few Feltiella. In addition, the corn plants turned brown and died within weeks, overwhelmed by the mites and overcrowded in the pots. Ludlow’s had one pot of corn that thrived and developed ears, and another that died. The pot that died had been moved, while the thriving corn had roots that went into well-fertilized earth under the pot.

The most alarming result of the study was when Sandy Menasha observed that the Banks Grass Mite damaged the bean leaves as well as the corn leaves. We had not been aware that this mite could attack broad leaved plants until that happened.

Alternative plants and predators for the banker plant system should be considered. Throughout the experiment small predatory beetles naturally colonized some BGM mite infested corn and may be good predators for this banker plant system. In all tunnels, except for Garden of Eve, Feltiella appeared on tomatoes and beans more often than the corn banker plant.

Two positive outcomes of the study were

bean trap plants were demonstrated at all 4 sites, and were indicators of both two spotted spider mites and Feltiella, and

Feltiella was demonstrated readily colonizing both the control and the treated greenhouses.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary

Education/outreach description:

The study will be presented either as a Powerpoint or a poster at the International Organization of Biological Control Meeting of the Protected Crops working group in Canada in June 2017.

Project Outcomes

Project outcomes:

The system did not perform as hoped, and will not be cost effective for growers at the present time. In addition, we discovered that Banks grass mite can indeed attack and disfigure some broad-leaved plants, so it will not be as flexible as the aphid banker plant system, which has aphids that really do confine themselves to grasses.

However, it is possible that some other combination of plants and BGM will be found to work better.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Additional studies should focus on the BGM population threshold required to support Feltiella on corn, additional banker plants that may be more suitable for Feltiella, and the potential for predatory beetles in the BGM banker plant system. We also need to know which broad leaved plants the BGM attack before this system can be used broadly.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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